76 TILE DRAINAGE. 



water on both sides it might possibly go through the brick on 

 that principle of chemical physics known as osmose (endosmose 

 and exosmose), by which two liquids on different sides of a blad- 

 der or membrane partition mix through the membrane, which is 

 impervious to either alone ! Or, if not on this principle, I thought 

 perhaps the water on both sides of the tile might relieve the 

 retentive force of the capillary attraction and so let the water 

 through, while, owing to the greater height on one side, the force 

 of gravity might push it through. The theory seemed all right 

 to explain the alleged facts about cistern filters, but it wouldn't 

 work on the tile. I filled the tile full and the pail half full, but 

 not a drop would go through, influenced either by gravity, capil- 

 lary attraction, or the molecular attraction called osmose. Not 

 the fraction of a teaspoonful could I get to go through in some 

 twelve hours of time, under all the different circumstances. And 

 I may add that, in the former experiments together with Prof. 

 Lord,' we let the water stand for days in a rather damp basement, 

 and not a drop came through. But in a dry wind that evapo- 

 rated the dampness from the moist surface of the tile, the capillary 

 attraction would supply the place of the moisture thus evaporated. 



Now, the tiles experimented 'with in both these cases were sim- 

 ply medium-burnt brick-clay tiles. But if the land is not drained 

 until the water goes through the walls of the tiles (except in case 

 of flaws or " pin-holes"), it will never be drained ; for a tile, so 

 porous that its walls would suck in one-fifth of its interior con- 

 tents, was so impervious that it would not let the decimal of a 

 teaspoonful pass through in twelve hours. 



I next addressed myself to ascertaining about how fast the 

 water can ge't in at the joints. I set another four-inch tile on 

 end on the one that was closed at the bottom, and was full and 

 saturated ; and I held it firmly down while my man filled it by 

 turning in water rapidly from a full pail ; and when the tile was 

 even full he cried k * Now ! " and my son and I timed it until it 

 had all run out at the joint just five seconds eight gallons per 

 minute ! But Gisborne, one of the earliest and best authorities, 

 figures that, with laterals 36 feet apart, the drains would remove 

 an inch of rainfall in 13 hours if each tile-junction will admit 

 two-thirds of a tablespoonful per minute ! And our tile admitted 

 (or let out) eight gallons per minute, under a pressure varying 

 from one foot perpendicular of water down to nothing several 

 hundred times as fast as need be. 



I have written pretty fully, in hopes of exploding the old idea 

 that the water soaks through the tiles. Makers of soft tiles seem 

 still to believe it, and some buyers too. Waring and other author- 

 ities on drainage state the case correctly. Waring says (' Drain- 

 ing for Profit and Health, " p. 77) : tfc They " that is, brick-clay 

 tiles" are porous to the extent of absorbing a certain amount of 

 water, but their porosity has nothing to do with their use for 

 drainage. For this purpose they might as well be of glass. The 

 water enters them, not through their walls, but at their joints, 



